Centrifugal elutriation involves the separation of cells or other particles by subjecting them to two opposing forces within a separation chamber. The two forces that the particles are subjected to are: (a) the centrifugal field generated by a spinning rotor and (b) a viscous drag of a fluid flowing in the opposite (centripetal) direction.
The two forces are counterbalanced in order to separate the particles. Each particle tends to migrate to a zone where its sedimentation rate is balanced by the flow rate of the fluid through the separation chamber. Because the chamber's geometry produces a gradient of flow rates from one end of the chamber to the other end, cells within a wide range of different sedimentation rates can be held in suspension. By increasing the flow rate of the elutriation fluid in steps, or decreasing the rotor speed, successive populations of relatively homogeneous cell sizes can be washed from the chamber. Each population will contain cells or particles which are larger or more dense (i.e., faster sedimentating) than those of the previous fraction. The principles of centrifugal elutriation are well known and can, for example, be found discussed in a publication entitled "Centrifugal Elutriation of Living Cells an Annotated Bibliography", publication TS-534-C, published by the Beckman Instruments, Inc., Spinco Division, P.O. Box 10200, Palo Alto, Calif. 94304. The above reference publication is herein incorporate by reference.
There is a great deal of prior art describing various types of rotors for use in centrifuges. For example, U.S. Pat. No. 4,670,002 (Koreeda) and U.S. Pat. No. 4,350,283 (Leonian) describe rotors for centrifuges. The rotors shown in these patents include one or more elutriation chambers and a rotating seal for passing fluid to and from the motors. The elutriation chambers form an integral part of the rotor thus the rotor assembly is quite heavy. With rotors of the type shown in these patents, when a separation run is completed and one wants to sterilize the chamber, one must remove the entire rotor from the machine and place it in the autoclave sterilization unit.
Other centrifugal elutriation rotors are known wherein the collection chambers can be separated from the rotor and placed in an autoclave without placing the entire rotor in the autoclave. However, in such units the rotating seal is part of the basic rotor assembly and in order to clean the rotating seal one must place the entire rotor in the autoclave.